Method and apparatus for separating particulate materials

ABSTRACT

A mixture of relatively malleable and relatively friable materials in particulate form within a given initial size range is separated into a fraction composed essentially of the malleable materials and a fraction composed essentially of the friable materials by first subjecting the mixture, in a vibratory mill, to forces effective to break up the particles of the friable fraction into sizes constituting a range substantially below the initial size range without substantially breaking up the particles of the malleable material and then separating the mixture according to size.

United States Patent Mitchell, III [451 July 1 1, 1972 54] METHOD AND APPARATUS FOR 3,510,074 5/1970 Edwards et a1. ..241/1s3 SEPARATING PARTICULATE 1 32%; 3; i 5

, ove MATERIALS 1,930,684 10/1933 Kramer.... .24l/l 5 X [72] invemor; Chauncey L Mitchel], n Fair Haven, 3,037,711 6/1962 Businger ..24l/24 Primary Examiner-Granville Y. Custer, Jr. [73] Assignee: Electronic Assistance Corporation, Red Attorney-Brumbaugh, Graves, Donohue & Raymond Bank, NJ.

57 ABSTRACT [22] Filed: July 6, 1970 1 A mixture of relatively malleable and relatively friable materi- PP 52,506 als in particulate form within a given initial size range is separated into a fraction composed essentially of the malleable materials and a fraction composed essentially of the friable [52] US. Cl ..24l/20, 241/24, 2244117789, materials y first subjacting the mixture in a vibratory mm, to 1 forces efiective to break up the particles of the friable fraction Cl- ..B02c into Sizes constituting a range substantial y below the [58] Fleld of Search ..24l/3, 15, 24, 46, 46.02, 46.15, Size range without Substantially breaking up the particles f 21, 38 the malleable material and then separating the mixture according to size. [56] References Cited 12 Claims, 3 Drawing Figures UNITED STATES PATENTS 979,180 12/1910 Lovett ..241/3 VIBRATORY MILL WATER EXTRACTOR METAL lMPURlTIES P'ATENT'EDJUL 11 I972 3, 675,859

onoss -I0 I6 WATER IZa I80 MIXER VIBRATORY WATER /24 EXTRACTOR SEPARATOR "'26 ZBU UZU l l METAL IMPURITIES INVEILWL R CHAUNCEY L. M lTCHELLJfl ATTORNEYS METHOD AND APPARATUS FOR SEPARATING PARTICULATE MATERIALS BACKGROUND OF THE INVENTION This invention relates to a method of processing a mixture of particulate malleable and friable materials into a fraction composed essentially of the malleable materials and a fraction composed essentially of the friable materials, and apparatus for carrying out the method.

The separation of mixtures of particulate materials of different kinds may be carried out in various ways, depending upon the characteristics of the material. For example, if the particles of one material in the mixture are of a different size from the particles of the other material, separation by size, such as by screening, is appropriate to recover the differing fractions. If one of the materials has a specific gravity differing appreciably from another in the mixture, various ways of separating the fractions on the basis of the differences in specific gravity can be used. There are, however, various mixtures of materials encountered in industrial processes that do not lend themselves to conventional separation techniques that have been proposed and used heretofore.

An example of a separation problem that has not been successfully solved heretofore occurs in the refining of various nonferrous metals. Many nonferrous metals are refined by smelting, and the smelting procedure results in the formation of a scum on the top of the metal bath, the scum being generally termed dross. The dross is skimmed or otherwise removed from the metal bath continuously or periodically in most smelting processes, and in many instances the dross contains not only impurities separated from the metal but a substantial content of the metal itself. Although in the processing of some nonferrous metals by smelting, the dross can be processed to recover some of the metal content, complete recovery is frequently impossible or at least impractical from an economic standpoint.

A particular example of a loss of substantial values of metal with the dross occurs in the processing of aluminum, either in the original recovery process, in the smelting of aluminum pig, or scrap, or in the refining of an alloy. In some instances, the dross skimmed from the surface of the molten metal is removed and either stored or disposed of without any processing to recover the aluminum content. However, equipment has been proposed and used for recovering some of the metal. One example of a technique and apparatus for recovering part of the metallic aluminum is described in U.S. Pat. No. 2,481,59l, and U.S. Pat. No. 3,417,930 and other patents referred to therein also describe apparatus and equipment for recovering aluminum from dross.

A process carried out according to U.S. Pat. No. 3,417,930 results in a particulate dross from which some of the metallic aluminum is recovered by violent shaking which causes a preliminary separation of molten aluminum. The aluminum solidifies on a cooling surface of a conveyor, and subsequent fragmentation of the dross results in a further separation and recovery of metallic aluminum. However, the process and equipment still leaves a substantial output of finely divided particles (called fines") containing a mixture of particulate metallic aluminum, either in discrete particles essentially free of impurities or particles encased partially or fully within a coating of impurities, and particulate impurities, and such fines are not susceptible to further recovery by any economically practical method.

SUMMARY OF THE INVENTION- There are provided, in accordance with the invention, a method and apparatus for separating particulate materials, particularly finely divided particles composed, as is the case with the dross resulting from the processing of certain nonferrous metals such as aluminum, or relatively malleable materials and relatively friable materials. In general, the method and apparatus of the invention are applicable to such mixtures in instances where the materials are within a given size range and thus cannot be separated by screening or other classification based on size. Also, the invention can be used where the particles are bound together, such as in the case with much of the dross fines in which the metal particles are fully or partially encapsulated within a crust of the impurities. In accordance with the method, the materials are subjected to forces effective to break up the friable materials into sizes constituting a range substantially less than the initial size range of the mixture without substantially breaking up the malleable materials and thereafter separating the material according to size to obtain a portion composed predominantly of the malleable fraction and a portion composed predominantly of the friable fraction. Where the malleable materials are partially or fully encased in the friables, the process also involves as aspect of braking the malleables free.

- A preferred way of treating the mixture to break up the friable materials in the manner described above is to process them in vibratory mills, and particularly advantageous results have been obtained using vibratory mills constructed according to U.S. Pat. No. 3,510,074, issued May 5, 1970. Equipment of that type is manufactured by the present assignee. The vibratory mills, according to the application, are composed of conduits charged with grinding media and driven by vibratory motion that is substantially along a single axis. In a preferred embodiment, the mill includes a number of substantially parallel conduits, which are usually connected together in series, and the media to be ground is pumped through the conduits in a liquid suspension. Preferably, the bottoms of the conduits are corrugated in a manner such that a bottom layer of steel, ceramic or other grinding media is trapped with the result that a tangential force is generated during each half cycle of vibratory motion. The force is propagated upward through the layers of media and produces large horizontal and vertical forces that deliver energy throughout the cross section of the conduit and provide unusually effective and efficient grinding.

According to an exemplary embodiment of the invention, as applied to aluminum dross, the particulate dross, which is composed of an aluminum fraction and an impurities fraction in which the aluminum fraction is relatively malleable and the impurities fraction is relatively friable, is mixed with a liquid, e.g., water and is pumped into the mill where it is subjected to the action of the media to the end that the friable materials are ground into a very fine size, substantially less than the initial size range of the dross being processed. Soluble constituents of the friable materials will be dissolved in the liquid, their solubility being enhanced by their fineness and the vibratory action of the mill.

At the same time, the relatively malleable fraction, the aluminum content of the dross, undergoes deformation by the action of the grinding media with little tendency to be broken up. In general, the aluminum particles in the dross are deformed into a generally flat, disc-like configuration with the result that their effective size is actually increased. Consequently, the output discharged from the mill is composed of finely ground friable materials, predominately the impurities of the dross, relatively larger sized particles of aluminum, and a liquid carrying the solubles. The mixture is then separated by drawing off the liquid solution and then dividing the remaining solids according to size by appropriate equipment, such as screens. For example, the material discharged from the mill can be delivered to a filter to separate the solids from the liquid and the solids fed directly to one or move screens which collect the larger sized aluminum particles while passing the finely divided impurities.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be made to the following description of exemplary embodiments, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating the overall method and apparatus of the invention;

FIG. 2 illustrates a portion of a vibratory mill employed in the invention; and

FIG. 3 is a cross section through the device of FIG. 2 illustrating the action of the vibratory mill.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Referring to FIG. I of the drawings, the mixture of relatively malleable and relatively friable materials desired to be separated is supplied, such as through a hopper 10, which may be on line with a prior industrial process involving the materials, through a supply conduit 12 to a suitable mixing device 14 where the particulate materials are blended with a liquid, which may be water, oil or any suitable liquid such as a process liquid from an upstream or downstream operation in the commercial process. The liquid is supplied from a source 16 through a conduit 18, and the amounts of the material and liquid are controlled by valves 12a and 18a.

The suspension of the particulate materials in the liquid is then delivered to a device for subjecting the materials to forces effective to break up the friable materials in the mixture into substantially smaller sized particles without substantially breaking up the relatively malleable materials. In the embodiment illustrated, the device for so processing the materials is a vibratory mill 20, utilizing spherical or other shaped mediain the vibrating chamber or chambers, and the suspension of materials and liquid is delivered under pressure to the mill 20 by either pumping or gravity feed. The ratio of liquid to solid is determined by the size of the particles and the dimensions of the mill and is adjusted to provide optimum throughput.

As mentioned above, particularly effective results are obtained with a vibratory mill of the type described and illustrated in U.S. Pat. No. 3,5 10,074. A single conduit or vibratory chamber according to that patent is shown in FIG. 2, by way of illustration. The suspension is introduced at the end marked INPUT as the conduit vibrates rapidly in the directions indicated by the transverse arrows. The treated material is withdrawn at the OUTPUT end. The cross-sectional view of FIG. 3 depicts in dotted line 1 the effectively corrugated bottom of the conduit formed by a plurality of parallel rods, which produce the enhanced random motion of the media that contribute to its improved action.

After undergoing the action of the mill, the material is discharged through an output conduit 22 to a liquid extraction or dewat ering stage 24 where the liquid, including such constituents of the material as may be dissolved in it, is removed from the suspension. This stage may be, for example, a centrifuge or a filter arrangement. The remaining solids preferably are dried in the dewatering stage and then are fed to the separator 26 where they are separated according to size into a fraction composed predominantly of the malleable material, which is discharged through one outlet 28 from the separator, and a fraction composed predominantly of the finely divided friables which is discharged through an outlet 30 from the separator.

The following example is representative of the application of the method and apparatus of the invention.

Aluminum dross within a size range passing an 8 mesh screen and retained on a 48 mesh screen (U.S. series) was mixed with water at a ratio of one gallon of water per pound of dross and delivered at a rate of 360 pounds of particulate material per hour to a machine of the type described in the specification and illustrated in FIGS. 9 to 11 of U.S. Pat. No. 3,510,074. The machine was operated at a frequency of 40 cycles per second and at an amplitude (taken as the total displacement of the mill conduits from the end of their travel in one direction to the end of travel in the other direction) of one-half inch, the horsepower input to the unit being on the order of 20 horsepower per cubic foot capacity. The resonant mill was charged with grinding media in the form of steel pellets of elongated shape having a number of facets merging at somewhat blunted corners. This form of media provided a degree of line contact, and previous experimentation demonstrated that particularly good results were obtained with this media. A single conduit only of the mill was employed.

The aluminum content of the dross supplied to the machine was approximately 70 percent by weight. The material discharged from the mill was screened through a 48 mesh screen, and the material retained on the screen amounted to 216 pounds per hour. Tests on the material indicated that it contained approximately percent aluminum, or pounds per hour, the aluminum particles being of flattened disc-like configuration having a typical ratio of diameter to thickness of 4 to l, e.g., a diameter of one-eighth inch to a thickness of one thirty-second inch.

It will be understood that various changes in the abovedescribed method and apparatus will occur to those skilled in the art without departing from the spirit of the invention. For example, the dewaten'ng and separating steps may be combined and types of vibratory mills other than that disclosed may be employed. It is intended that the invention be limited only by the scope of the appended claims.

I claim:

1. A method of processing a mixture of relatively malleable and relatively friable materials in particulate form, the particles being within a given initial size range, comprising the steps of suspending the mixture in a fluid, subjecting the mixture to forces effective to break up the friable particles into sizes constituting a range substantially below the initial size range and causing said malleable particles to increase their size to a range substantially above said initial size range, causing soluble friable particles to dissolve in the fluid and thereafter separating the material according to size to obtain a portion composed predominantly of the malleable fraction and a portion composed predominantly of the insoluble friable fraction.

2. A method according to claim 1 wherein the mixture is treated in a vibratory mill, the material being suspended in a liquid and conducted through a conduit containing a grinding media and vibrated substantially along an axis transverse to the conduit axis.

3. A method of processing particulate material having an initial particle size range and composed of a relatively malleable metal fraction and a relatively friable impurities fraction, some of which may be soluble, comprising the steps of delivering a suspension in a liquid of the mixture to a vibratory mill, the mill having a conduit for the material containing a grinding media, subjecting the conduit to vibratory motions substantially along a single axis thereby to impart motion to the grinding media and to subject the mixture to impact and shear forces sufficient to break up the impurities fraction to a size range substantially less than the initial size range and to deform the particles of the metal fraction into generally disclike bodies having a size range substantially greater than the initial size range, discharging the suspension from the vibratory mill, and thereafter separatingthe discharged suspension mixture into a liquid component including solubles, and on the basis of size, into a fraction composed predominantly of the malleable metal particles and a fraction composed of the friable impurities and the suspension liquid.

4. A method according to claim 3 wherein the mixture of particulate materials is suspended in water in an amount of from about 1 pound of particulate material to 1 gallon of liquid.

5. A method according to claim 3 wherein the particulate material is within a size range such as to pass an 8 mesh screen and to be retained on a 48 mesh screen.

6. Apparatus for processing a mixture of relatively malleable and relatively friable materials in particulate form, the particles being within a given initial size range, comprising means for suspending the particles of said mixture in a fluid, means for subjecting the suspended mixture to forces effective to break up the friable particles into sizes constituting a range substantially below the initial size range and causing soluble friable particles to dissolve in the fluid without substantially breaking up the malleable particles, means for removing the fluid including the dissolved friables, and means for separating the remaining materials according to size to obtain a portion composed predominantly of the malleable fraction and a portion composed predominantly of the insoluble friable fraction.

7. Apparatus according to claim 6 wherein the means for breaking up the friables is a grinding device.

8. Apparatus according to claim 7 wherein the grinding device is a vibratory mill.

9. Apparatus according to claim 8, wherein the vibratory mill is a ball mill comprising at least one conduit for the material charged with grinding media and means for vibrating the conduit along substantially solely an axis. 

2. A method according to claim 1 wherein the mixture is treated in a vibratory mill, the material being suspended in a liquid and conducted through a conduit containing a grinding media and vibrated substantially along an axis transverse to the conduit axis.
 3. A method of processing particulate material having an initial particle size range and composed of a relatively malleable metal fraction and a relatively friable impurities fraction, some of which may be soluble, comprising the steps of delivering a suspension in a liquid of the mixture to a vibratory mill, the mill having a conduit for the material containing a grinding media, subjecting the conduit to vibratory motions substantially along a single axis thereby to impart motion to the grinding media and to subject the mixture to impact and shear forces sufficient to break up the impurities fraction to a size range substantially less than the initial size range and to deform the particles of the metal fraction into generally disc-like bodies having a size range substantially greater than the initial size range, discharging the suspension from the vibratory mill, and thereafter separating the discharged suspension mixture into a liquid component including solubles, and on the basis of size, into a fraction composed predominantly of the malleable metal particles and a fraction composed of the friable impurities and the suspension liquid.
 4. A method according to claim 3 wherein the mixture of particulate materials is suspended in water in an amount of from about 1 pound of particulate material to 1 gallon of liquid.
 5. A method according to claim 3 wherein the particulate material is within a size range such as to pass an 8 mesh screen and to be retained on a 48 mesh screen.
 6. Apparatus for processing a mixture of relatively malleable and relatively friable materials in particulate form, the particles being within a given initial size range, comprising means for suspending the particles of said mixture in a fluid, means for subjecting the suspended mixture to forces effective to break up the friable particles into sizes constituting a range substantially below the initial size range and causing soluble friable particles to dissolve in the fluid without substantially breaking up the malleable particles, means for removing the fluid including the dissolved friables, and means for separating the remaining materials according to size to obtain a portion composed predominantly of the malleable fraction and a portion composed predominantly of the insoluble friable fraction.
 7. Apparatus according to claim 6 wherein the means for breaking up the friables is a grinding device.
 8. Apparatus according to claim 7 wherein the grinding device is a vibratory mill.
 9. Apparatus according to claim 8, wherein the vibratory mill is a ball mill comprising at least one conduit for the material charged with grinding media and means for vibrating the conduit along substantially solely an axis.
 10. Apparatus according to claim 9 wherein the conduit has a corrugated bottom surface such as to impose a generally tangential force on the grinding media that is propagated through substantially the entire cross section of the conduit.
 11. Apparatus according to claim 9 and further comprising means for blending the material with a liquid and means for conducting a blend of the material and liquid continuously into and out of the mill.
 12. Apparatus according to claim 6 wherein the means for separating the materials is a screen or screens. 